The dynamic interaction of an enzyme with its substrate occurs along a well-define catalytic pathway that consists of multiple, elementary steps. As this pathway is traversed, transient enzyme-substrate intermediates are formed. To fully understand the mechanism of enzyme catalysis, it is essential that both the detailed nature of the enzyme-substrate interaction and the structures of both th enzyme and substrate in each of these intermediates be elucidated. In the past, studies of intermediates have proven difficult because of their brief lifetime and low concentration. Furthermore, methods capable of providing information about structure and interactioss within the active sites of enzymes in solution have not been developed. The proposed research combines two areas of current research to overcome these problems. Subzero temperatures and cryosolvents will be used to accumulate intermediates in high concentrations for periods of time that permit their spectroscopic study. Resonance Rama Spectroscopy will then be used to study intermediates in which either the substrate or enzyme contains a chromophoric probe to yield vibrational spectra of parts of the active site. These spectra are capable of providing the needed structural information and, hence, this research promises to significantly advance our basic understanding of the mechanism of enzyme catalysis.